The basis of the presented investigations in this thesis is the modulation of signal inducers and their respective activated signaling cascades through intrinsic antagonistic feedback- and/or feed... Show moreThe basis of the presented investigations in this thesis is the modulation of signal inducers and their respective activated signaling cascades through intrinsic antagonistic feedback- and/or feed forward-loops. In particular, signal inducers of the transforming growth factor-_ superfamily were investigated on their impact on tissue development and maintenance. Thereby, the main focus lies on a group of proteins that are known as bone morphogenetic proteins (BMPs). Due to their wide impact, Dr. H. Reddi recently proposed a more suitable name to this cytokines: body morphogenetic proteins. The distinct terminology is also reflected in this book. Not only does this book discuss the impact of BMP signal modulation on osteoblast differentiation, it also focuses on BMPs as potential inducers of signaling drifts in fibrotic traits. Interestingly, BMPs can relay signals with different outcomes. They can be signal triggers themselves as investigated in the case of osteoblast differentiation, but they can also arrest signaling cascades, as shown for TGF-_ induced fibrosis. Up to date, more than fifteen different BMPs are known. One aim of this book is to biochemically characterize different BMPs on their potential to relay signals and how this signals can be governed to yield a specific medical benefit. It is well known that BMPs are tightly regulated on diverse interfaces throughout the cell. Thereby, the presented investigations focus on innate extracellular signaling modulators, as well as on synthetic small molecule inhibitors that have the potential to facilitate the development of new treatment strategies of certain human diseases. Show less
Sclerostin is expressed by osteocytes and has catabolic effects on bone. It has been shown to antagonize bone morphogenetic protein (BMP) and/or Wnt activity, although at present the underlying... Show moreSclerostin is expressed by osteocytes and has catabolic effects on bone. It has been shown to antagonize bone morphogenetic protein (BMP) and/or Wnt activity, although at present the underlying mechanisms are unclear. Consistent with previous findings, Sclerostin opposed direct Wnt3a-induced but not direct BMP7-induced responses when both ligand and antagonist were provided exogenously to cells. However, we found that when both proteins are expressed in the same cell, sclerostin can antagonize BMP signaling directly by inhibiting BMP7 secretion. Sclerostin interacts with both the BMP7 mature domain and pro-domain, leading to intracellular retention and proteasomal degradation of BMP7. Analysis of sclerostin knock-out mice revealed an inhibitory action of sclerostin on Wnt signaling in both osteoblasts and osteocytes in cortical and cancellous bones. BMP7 signaling was predominantly inhibited by sclerostin in osteocytes of the calcaneus and the cortical bone of the tibia. Our results suggest that sclerostin exerts its potent bone catabolic effects by antagonizing Wnt signaling in a paracrine and autocrine manner and antagonizing BMP signaling selectively in the osteocytes that synthesize simultaneously both sclerostin and BMP7 proteins. Show less
Bone morphogenetic proteins (BMPs) are used clinically to induce new bone formation in spinal fusions and long bone nonunion fractures. However, large amounts of BMPs are needed to achieve these... Show moreBone morphogenetic proteins (BMPs) are used clinically to induce new bone formation in spinal fusions and long bone nonunion fractures. However, large amounts of BMPs are needed to achieve these effects. BMPs were found to increase the expression of antagonists, which potentially limit their therapeutic efficacy. However, the relative susceptibility of osteoinductive BMPs to different antagonists is not well characterized. Here we show that BMP-6 is more resistant to noggin inhibition and more potent in promoting osteoblast differentiation in vitro and inducing bone regeneration in vivo when compared with its closely related BMP-7 paralog. Noggin was found to play a critical role as a negative feedback regulator of BMP-7 but not BMP6-induced biological responses. Using BMP-6/7 chimeras, we identified lysine 60 as a key residue conferring noggin resistance within the BMP-6 protein. A remarkable correlation was found between the presence of a lysine at this position and noggin resistance among a panel of osteoinductive BMPs. Introduction of a lysine residue at the corresponding positions of BMP-2 and BMP-7 allowed for molecular engineering of recombinant BMPs with increased resistance to noggin antagonism. Show less
